Spark plug for internal combustion engine

Abstract

A spark plug 1 includes a housing 2 , an insulator 3 , a center electrode 4 held inside the insulator 3 such that a distal end portion 41 protrudes, a ground electrode 5 including a standing portion 51 and an opposing portion 52 , and a guide member 22 that has a guide surface 221 facing the standing portion 51 of the ground electrode 5 and functions to guide a flow of an air-fuel mixture in a combustion chamber of an internal combustion engine to a spark discharge gap G formed between the center electrode 4 and the opposing portion 52 of the ground electrode 5 . The opposing portion 52 of the ground electrode 5 has an opposing surface 521 that opposes the center electrode 4 , a back surface 522 on the opposite axial side to the opposing surface 521 , and a pair of side surfaces 523 and 524 that connect the opposing surface 521 and the back surface 522 . Of the pair of side surfaces 523 and 524 , at least the side surface 523 on the guide member 22 side is formed so as to make an obtuse angle with the opposing surface 521.

The invention claimed is: 
     
       1. A spark plug for an internal combustion engine, comprising:
 a tubular housing; 
 a tubular insulator held inside the housing; 
 a center electrode held inside the insulator such that a distal end portion protrudes; 
 a ground electrode including a standing portion that stands distalward from a distal end of the housing and an opposing portion that is bent radially inward from the standing portion and opposes the center electrode in an axial direction of the spark plug through a spark discharge gap formed between it and the center electrode; and 
 a guide member for guiding a flow of an air-fuel mixture in a combustion chamber of an internal combustion engine to the spark discharge gap, the guide member protruding distalward from the distal end of the housing at a different circumferential position from the ground electrode and having a guide surface that faces the standing portion of the ground electrode, 
 wherein 
 the opposing portion of the ground electrode has an opposing surface that opposes the center electrode, a back surface on the opposite axial side to the opposing surface, and a pair of side surfaces that connect the opposing surface and the back surface, and 
 of the pair of side surfaces, at least the side surface on the guide member side is formed so as to make an obtuse angle with the opposing surface. 
 
     
     
       2. The spark plug for an internal combustion engine as set forth in  claim 1 , further wherein
 the standing portion of the ground electrode has a radially inner side surface that faces the center electrode, a radially outer side surface on the opposite radial side to the radially inner side surface, and a pair of circumferential side surfaces that connect the radially inner side surface and the radially outer side surface, and 
 of the pair of circumferential side surfaces, at least the circumferential side surface on the guide member side is formed so as to make an obtuse angle with the radially inner side surface. 
 
     
     
       3. The spark plug for an internal combustion engine as set forth in  claim 1 , further wherein
 the opposing portion has, at an end on the opposite side to the standing portion, a small-width part that has a smaller width in a direction perpendicular to both the extending direction of the opposing portion and the axial direction of the spark plug than other parts. 
 
     
     
       4. The spark plug for an internal combustion engine as set forth in  claim 1 , further wherein
 the guide member has its distal end located flush with or proximalward from a distal end of the ground electrode and flush with or distalward from a distal end of the insulator. 
 
     
     
       5. The spark plug for an internal combustion engine as set forth in  claim 1 , further wherein
 the guide member protrudes parallel to the axial direction of the spark plug.